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The Mutation Problem
David Plaisted

There are a number of very serious problems with mutation rates that call the theory of evolution into question.  It has taken me a long time to appreciate the magnitude of these problems.  These problems with mutation rates do not seem to be appreciated by most biologists, and even the creationist sources I have read do not seem to comprehend the seriousness of the problems posed for the theory of evolution by the rates of mutation observed and assumed for evolution. I would encourage those among you who are taking biology courses to present this material to your instructors and see if they can give you an adequate answer to it.  If there are any mistakes in this article, please inform me of them (plaisted@cs.unc.edu).

  Population Genetics Background

First, I present some very general and simple results from population genetics.  For a justification of these results, see the article Population Genetics Made Simple at my web site,

http://tasc-creationscience.org/other/plaisted/www.cs.unc.edu/_plaisted/ce/index.html

or any text on population genetics.

The first result we need to know is simple and very surprising -- when a population is at equilibrium, then the chance that an individual (fertilized egg, or zygote) will have a new, harmful mutation not possessed by the parents as zygotes is smaller than the chance that the individual will die without offspring.  It doesn't matter how harmful the mutation is, since less harmful mutations will spread to more of the population.  Put another way, the chance that a zygote can survive and have offspring is less than the chance that it has no new harmful mutations, when the population is at equilibrium.  

The next point is that equilibrium should nearly be reached in a few hundred generations.  If the human population is not at equilibrium, then it must be very young (less than a few hundred generations) and created nearly perfect, without harmful mutations. The calculation of the time to equilibrium is sketched in the article on population genetics at my web site.  

Later we will argue that most harmful mutations will at least come to the birth.  In any species, individuals that are not able to reproduce will still require pregnancy and nurture, will consume food and occupy territory, and possibly compete for mates.  In addition to not being able to reproduce, these individuals will make it more difficult for the remaining population to survive.  Their genetic defects will be of many different kinds and will appear at many different stages of life.  If a species has a considerable fraction (say, half) of individuals with such defects, it would appear that the species could hardly survive due to the added burden.  

It is reasonable to assume that individuals with such defects not only cannot survive themselves, but also result in other individuals not being able to reproduce.  So we can assume (say) that for every ten such individuals, one other individual becomes unable to reproduce.  This means that if 10/11 of the population is defective in this way, then the population will die out no matter how many offspring each parent has.  

Now, suppose there is one harmful mutation per offspring on the average.  Then it follows that the chance of a zygote being free from a new, harmful mutation is 1/(2.718), or about 37 percent.  This means that at equilibrium, only 1/(2.718) of the zygotes can become reproducing adults.  Of the remaining 63 percent of the individuals, more than half will probably come to birth (as we argue below), meaning that there will likely be more defective births than defect-free births.  Even this seems like a rate of mutation that is unbearable, especially for higher organisms such as mammals.  

If there are three non-neutral mutations per offspring (a rate quoted on talk.origins), they are all most probably harmful, leading to only 1/(2.718)^3 of the zygotes that can reproduce.  This is only about 5 percent!!  

Now, about 10 percent of DNA is typically assumed to code for genes, and the rest is mostly non-functional.  A mutation to the functional DNA will change the amino acid more than 2/3 of the time, and if it does, the mutation will be harmful about 9/10 of the time or more (according to estimates by biologists).  Thus we can assume that 2/3 of the point mutations to functional DNA are harmful.  The non-functional DNA changes at the same rate as that at which mutations occur.

  Mutation Rates based on Observation  

From standard reference materials, observed mutation rates in humans appear to be between .5 and 4 per 100,000 gametes (sperm or egg).  The average is about one per 100,000 gametes among living organisms, but may be considerably higher.  For humans, the average is about four per 100,000 gametes.  This would lead to eight harmful mutations per zygote (fertilized egg) on the average, at 100,000 genes in the human.  This would mean that at equilibrium, only about 1/(2.718)^8 or less than 1/3000 of the zygotes could develop into reproducing individuals!!  

This can only be reconciled with reality by assuming that the human race is only a few hundred generations old at most, initially defect-free, or that the harmful mutations are clustered in a few individuals who are very unlikely to have surviving offspring.  In the latter case, the number of effective mutations available for evolution would be much smaller.

  Mutation Rates Based on Evolution  

The talk.origins site mentions a rate of evolution for silent sites at 4.61 per billion years.  It is reasonable to assume that this is due to point mutations at this rate, since silent sites are essentially neutral (not changing the amino acid coded).  Mammals typically have genomes of at least 1.5 billion base pairs, and assuming 10 percent of this is functional, there would be 150 million base pairs of functional DNA.  Assuming a mutation per base pair every 200 million years (4.61 per billion years), this means 150 million point mutations in the functional DNA and at least 100 million harmful mutations every 200 million years, since 2/3 of the mutations are harmful.  This is a harmful mutation every other year on the average. Counting both parents, each zygote would have one harmful mutation per year.  With a one year generation time, this would be an intolerable rate of mutation, as mentioned above (only 37 percent of the zygotes could have offspring).  This is even worse for organisms that have longer generation times.  If one assumes that the rate of mutation slowed down for these latter organisms, then it had to be even higher for the earlier ones.  

  Human Mutation Rates Based on Abortions and Defects

The following facts are obtainable from standard reference materials:  

15 - 20 percent of diagnosed pregnancies miscarry.  Up to 60 percent are due to faulty chromosomes.  This includes all miscarriages after the first two weeks of pregnancy.  Before that, one can only speculate.  It is thought that more than 60 percent of conceptions are spontaneously aborted, including spontaneous abortions during the first two weeks.  40 to 50 percent of spontaneous abortions have chromosomal abnormalities.  3 to 4 percent of newborns have birth defects.  At least half have a genetic contribution.  About 7 percent of all births show some mental or physical defect.  Genetic defects (often minor) are present in 10 percent of adults.

The fertilized egg implants in the uterus on about the seventh day.  It then causes hCG to be produced, which prevents menstruation. Cells in the fetus begin to differentiate after about the first week. After four weeks, only very primitive arms, eyes, legs, lungs, brain, and heart (mostly just stubs) appear.  After about two months the fetus' organs begin to function, but not fully till after birth.

Now, we attempt to analyze the above data.  Only a small percentage of genes are expressed in eggs and sperm and during the first two weeks of pregnancy.  So the percentage of genetic defects causing abortions then should be very small.  Later, about 15 to 20 percent of pregnancies miscarry, and this can be caused by chromosomal abnormalities and other causes.  Counting birth defects and adults with defects, some of which are minor and do not prevent reproduction, there should be about 5 percent of adults that cannot reproduce due to genetic defects.

Since the womb is such a sheltered environment, and the fetus will likely survive if it develops a circulatory system, one would expect most defective individuals to at least be born.  This means that at most 5 percent of zygotes will be aborted due to point mutations.  So it is reasonable to estimate the total percentage of zygotes that cannot reproduce due to point mutations at about 10 percent and possibly much less.  It would seem difficult to stretch the figures to make this more than about 30 percent in any event.

Therefore, based on genetic defects, the rate of harmful mutation in humans can be at most about 5 percent per generation (considering both parents gives 10 percent), possibly 10 or 15 percent per parent at the most.  This conflicts sharply with the rate of 3 or 4 mutations per generation that is often quoted.  It conflicts even more with 4.61 mutations per billion years, which would imply 15 per generation, or 30 harmful mutations per zygote, with only an astronomically small portion surviving to reproduce.

  Implications for the Ape Human Split

Now, apes and humans are thought to have split about 10 million years ago, and have about a 2 percent difference in DNA.  The human genome has about 3 billion base pairs and about 300 million base pairs of functional DNA (assuming 10 percent of 3 billion base pairs are functional).  Assuming that most of this 2 percent change is non-functional DNA, this implies a rate of evolution of one percent in 10 million years, which implies 3 million point mutations in 10 million years in the functional DNA.  Two-thirds of these would be harfmul, or, 2 million in 10 million years.  This is about one point mutation in the functional DNA every five years, or about 6 every generation.  Counting both parents, this gives 12 mutations per zygote, with a chance of only 1/(2.718 ^ 12) (less than 1 in 100,000) that a zygote will survive and be able to have offspring at equilibrium.  Of course, this is ridiculous.

How much must we reduce the functional DNA to make this acceptable?  It would have to be at least a factor of 12, to about 25 million base pairs (less than one percent of the DNA).  This would imply one harmful mutation per zygote, and would contradict estimates that 10 percent of the DNA is functional.  Typical genes have 1000 base pairs, so this would be 25,000 genes.  Even this rate of mutation is much too high, so there would probably have to be only about 15,000 genes.  A typical cell has over 10,000 proteins, so this is about the number of genes needed for a single cell.  So this is too few to specify a complete human being.  It also conflicts with estimates that humans have 100,000 genes.

How long ago would apes and humans have to split to allow evolution to have occurred?  It would have to be 12 times 10 million years, or 120 million years.  Even this is too high a mutation rate, as mentioned earlier.  And at the current rate of about 5 percent mutation, it would have to be about two billion years.  If the mutation rate was faster in the past, one wonders why it slowed down.

Another possibility is that the rate of mutation really is very low, and that the divergence in DNA is due to a few mutations that change many base pairs (such as inversions or copyings).  This seems unlikely, but we will soon know from DNA sequencing.  Also, if the divergence in silent sites between apes and humans is about 2 percent, which seems likely, this implies that such a rate of mutation did take place, and would seem to refute evolution.

   General Comments

I'm not interested in furthering anyone's agenda, but people do deserve to know the problems with the theory of evolution.  I also don't favor the teaching of religion in public schools.  However, the fact that evolution is taught in tax-supported schools and claimed to be scientifically supported gives it a greater burden of proof.

I rarely read talk.origins, so would appreciate any comments sent to me at plaisted@cs.unc.edu.  Other arguments problematical to the theory of evolution may be found at my web site (listed above).

http://tasc-creationscience.org/other/plaisted/www.cs.unc.edu/_plaisted/ce/index.html

 

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